/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.pinot.core.query.prefetch;

import java.util.Optional;
import java.util.concurrent.atomic.AtomicReference;


public class FetchPlannerRegistry {
  private static final AtomicReference<FetchPlanner> REGISTRATION = new AtomicReference<>(null);

  private FetchPlannerRegistry() {
  }

  private static final class Holder {
    public static final FetchPlanner PLANNER =
        Optional.ofNullable(REGISTRATION.get()).orElseGet(DefaultFetchPlanner::new);
  }

  /**
   * Provides a custom planner to replace the default one when server starts up.
   *
   * @param planner a custom fetch planner overwriting the default one.
   * @return true, if this is called for the first time.
   */
  public static boolean registerPlanner(FetchPlanner planner) {
    return REGISTRATION.compareAndSet(null, planner);
  }

  public static FetchPlanner getPlanner() {
    return Holder.PLANNER;
  }
}
